The present invention relates to a combustion apparatus used, for example, in a gas turbine combustion method in such combustion apparatus and, more particularly, a combustion apparatus including a liner forming a combustion chamber, with an air film forming means for protecting the liner from the hot combustion gas.
A combustion apparatus of the aforementioned type generally includes a combustor liner which forms a combustion chamber, with the with liner being provided with various cooling means for protecting the liner from the hot combustion gas.
One cooling means includes a film of air, with air being introduced into the combustor through an air film forming means provided in the liner portion so as to always form a layer of air film on the inner wall of the liner. The air layer effectively prevents the heat in the combustion zone from reaching the liner and carries the heat away from the liner itself.
The above described cooling method offers a high cooling efficiency with a small quantity of air so as to effectively prevent overheating of the liner, since the air not only carries the heat away from the liner but also interrupts heat transfer to the liner, unlike a cooling method in which the heated liner is merely cooled. In addition, this method is simple in its arrangement and practical, so that it has been used widely.
In this cooling method, it is important that a uniform layer of air film is always formed over the entire area of the inner wall of the liner.
This of course requires an arrangement for forming such a uniform air film. However, what is more important is that the air film is not broken or punctured by the swirling flow of combustion gas in the combustion chamber formed by the liner. In the combustor of this type, the swirling flow is imparted to the feeding mixed gas, in order to attain a better mixing of fuel with air and to facilitate holding of the flame. Consequently, the combustion gas also becomes a part of the swirling flow, so that the air film is easily broken by this swirling combustion gas.
In recent years, there is a trend to use low caloric fuels such as blast furnace gas or the like. When such a fuel is used, the flow rate of the fuel to be supplied is increased with the result that the diameter of a nozzle for jetting the fuel is also increased. Consequently, the size of the swirler for imparting the swirling flow to the feeding gas is increased correspondingly, so that the influence of the combustion gas flow extends to the vicinity of the liner's inner wall thereby resulting in an easy breaking of the air film.
This problem would be eliminated by using a combustor liner having a greater diameter so as to reduce the influence of the combustion gas flow. Such a countermeasure, however, does not cope with the current demand for reduction in the size of the combustor liner. An increase in the liner diameter correspondingly increases the area of the liner surface which, in turn, requires a greater flow rate of the cooling air.